Abstract â–¡ 160

Our research focuses on mechanisms involved in the integrated control of cardiovascular and respiratory function. Head-up and head-down tilting is used to probe the competence of these mechanisms. The hypothesis of this study was that physiological responses to tilt would be diminished in infants whose risk for SIDS is increased due to maternal smoking and/or drinking during pregnancy.

Data were obtained from 202 infants born at the Indian Health Service Hospital in Pine Ridge, South Dakota (US). The Native American infants born on this reservation have approximately a 3-fold greater risk for SIDS. Information regarding smoking and drinking during pregnancy were obtained from medical records and questionnaires administered during pregnancy and after delivery. Group assignment to these categories was defined by whether the mother acknowledged any level of these activities at any time during pregnancy.

Infants were tested at 12-36 hours of age 30 min after feeding. They were swaddled and sleeping in the prone position. After a 15 min baseline period, the bassinet was slowly tilted (30 sec) to the 30°C head-up position. After 1 min in this position, the infant was returned to the flat position. After 1 min the infant was tilted, to the 30°C head-down position for 1 min. After returning to the flat position this sequence was repeated. HR change scores were computed as differences between the last 30 sec of the tilted position and the 30 sec baseline period immediately preceding tilting.

Results (right) showed that HR responses of infants at low risk (i.e. mothers age > 17, HCT > 33, no illicit drug use, gravida < 4, parity < 3, no smoking, no drinking, N=24) are significant (p < .01) in both directions and are not significantly different from infants measured in a low SES population in New York City. However, Pine Ridge infants with any of the above risk factors (N=166) did not have a significant response to the head-up tilt and tended to have smaller head-down tilt responses as well. Further stratification revealed that groups of infants whose mothers smoked but did not drink (SM: N=42), drank but did not smoke (AL: N=24), or did both (SM/AL: N=40) did not have significant changes in heart rate to the head-up tilts. In addition, the head-down responses were not significant in the latter two groups. (Figure)

figure 1

These findings will be discussed in the context of a proposed pathogenic model of SIDS in which environmental risk factors lead to a diminished capacity to compensate for decreases in blood pressure. (Supported by NICHD: HD32774)